In English modal verbs (such as will, would, can, could, shall and should) take what we call the zero infinitive. This is the form of the infinitive without the word 'to,' in front of it - for example 'win,' rather than 'to win.'
"I would win if we played the game again."
This rule also applies to two non-modal verbs. Those verbs are "to make," and "to let."
The sentence above uses the verb "to make," so it has to use the zero infinitive. This is why there is no 'to,' in front of laugh.